/*
 Copyright 2013 Microsoft Open Technologies, Inc.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
 package com.microsoftopentechnologies.acs.util; 

public final class Base64 {
    /**
     * The Base 64 Characters.
     */
    private static final String BASE_64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    /**
     * Decoded values, -1 is invalid character, -2 is = pad character.
     */
    private static final byte[] DECODE_64 = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 0-15
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, /*
                                                                             * 16- 31
                                                                             */
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, /*
                                                                             * 32- 47
                                                                             */
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, /*
                                                                             * 48- 63
                                                                             */
            -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, /* 64-79 */
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, /*
                                                                             * 80- 95
                                                                             */
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, /*
                                                                             * 96- 111
                                                                             */
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 /*
                                                                            * 112- 127
                                                                            */
    };

    /**
     * Decodes a given Base64 string into its corresponding byte array.
     *
     * @param data
     *            the Base64 string, as a <code>String</code> object, to decode
     *
     * @return the corresponding decoded byte array
     * @throws IllegalArgumentException
     *             If the string is not a valid base64 encoded string
     */
   public static byte[] decode(final String data) {
        int byteArrayLength = 3 * data.length() / 4;

        if (data.endsWith("==")) {
            byteArrayLength -= 2;
        } else if (data.endsWith("=")) {
            byteArrayLength -= 1;
        }

        final byte[] retArray = new byte[byteArrayLength];
        int byteDex = 0;
        int charDex = 0;

        for (; charDex < data.length(); charDex += 4) {
            // get 4 chars, convert to 3 bytes
            final int char1 = DECODE_64[(byte) data.charAt(charDex)];
            final int char2 = DECODE_64[(byte) data.charAt(charDex + 1)];
            final int char3 = DECODE_64[(byte) data.charAt(charDex + 2)];
            final int char4 = DECODE_64[(byte) data.charAt(charDex + 3)];

            if (char1 < 0 || char2 < 0 || char3 == -1 || char4 == -1) {
                // invalid character(-1), or bad padding (-2)
                throw new IllegalArgumentException("The String is not a valid Base64-encoded string.");
            }

            int tVal = char1 << 18;
            tVal += char2 << 12;
            tVal += (char3 & 0xff) << 6;
            tVal += char4 & 0xff;

            if (char3 == -2) {
                // two "==" pad chars, check bits 12-24
                tVal &= 0x00FFF000;
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
            } else if (char4 == -2) {
                // one pad char "=" , check bits 6-24.
                tVal &= 0x00FFFFC0;
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
                retArray[byteDex++] = (byte) (tVal >> 8 & 0xFF);

            } else {
                // No pads take all 3 bytes, bits 0-24
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
                retArray[byteDex++] = (byte) (tVal >> 8 & 0xFF);
                retArray[byteDex++] = (byte) (tVal & 0xFF);
            }
        }
        return retArray;
    }

    /**
     * Decodes a given Base64 string into its corresponding byte array.
     *
     * @param data
     *            the Base64 string, as a <code>String</code> object, to decode
     *
     * @return the corresponding decoded byte array
     * @throws IllegalArgumentException
     *             If the string is not a valid base64 encoded string
     */
    public static Byte[] decodeAsByteObjectArray(final String data) {
        int byteArrayLength = 3 * data.length() / 4;

        if (data.endsWith("==")) {
            byteArrayLength -= 2;
        } else if (data.endsWith("=")) {
            byteArrayLength -= 1;
        }

        final Byte[] retArray = new Byte[byteArrayLength];
        int byteDex = 0;
        int charDex = 0;

        for (; charDex < data.length(); charDex += 4) {
            // get 4 chars, convert to 3 bytes
            final int char1 = DECODE_64[(byte) data.charAt(charDex)];
            final int char2 = DECODE_64[(byte) data.charAt(charDex + 1)];
            final int char3 = DECODE_64[(byte) data.charAt(charDex + 2)];
            final int char4 = DECODE_64[(byte) data.charAt(charDex + 3)];

            if (char1 < 0 || char2 < 0 || char3 == -1 || char4 == -1) {
                // invalid character(-1), or bad padding (-2)
                throw new IllegalArgumentException("The String is not a valid Base64-encoded string.");
            }

            int tVal = char1 << 18;
            tVal += char2 << 12;
            tVal += (char3 & 0xff) << 6;
            tVal += char4 & 0xff;

            if (char3 == -2) {
                // two "==" pad chars, check bits 12-24
                tVal &= 0x00FFF000;
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
            } else if (char4 == -2) {
                // one pad char "=" , check bits 6-24.
                tVal &= 0x00FFFFC0;
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
                retArray[byteDex++] = (byte) (tVal >> 8 & 0xFF);

            } else {
                // No pads take all 3 bytes, bits 0-24
                retArray[byteDex++] = (byte) (tVal >> 16 & 0xFF);
                retArray[byteDex++] = (byte) (tVal >> 8 & 0xFF);
                retArray[byteDex++] = (byte) (tVal & 0xFF);
            }
        }
        return retArray;
    }

    /**
     * Encodes a byte array as a Base64 string.
     *
     * @param data
     *            the byte array to encode
     * @return the Base64-encoded string, as a <code>String</code> object
     */
    public static String encode(final byte[] data) {
        final StringBuilder builder = new StringBuilder();
        final int dataRemainder = data.length % 3;

        int j = 0;
        int n = 0;
        for (; j < data.length; j += 3) {

            if (j < data.length - dataRemainder) {
                n = ((data[j] & 0xFF) << 16) + ((data[j + 1] & 0xFF) << 8) + (data[j + 2] & 0xFF);
            } else {
                if (dataRemainder == 1) {
                    n = (data[j] & 0xFF) << 16;
                } else if (dataRemainder == 2) {
                    n = ((data[j] & 0xFF) << 16) + ((data[j + 1] & 0xFF) << 8);
                }
            }

            // Left here for readability
            // byte char1 = (byte) ((n >>> 18) & 0x3F);
            // byte char2 = (byte) ((n >>> 12) & 0x3F);
            // byte char3 = (byte) ((n >>> 6) & 0x3F);
            // byte char4 = (byte) (n & 0x3F);
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 18) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 12) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 6) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) (n & 0x3F)));
        }

        final int bLength = builder.length();

        // append '=' to pad
        if (data.length % 3 == 1) {
            builder.replace(bLength - 2, bLength, "==");
        } else if (data.length % 3 == 2) {
            builder.replace(bLength - 1, bLength, "=");
        }

        return builder.toString();
    }

    /**
     * Encodes a byte array as a Base64 string.
     *
     * @param data
     *            the byte array to encode
     * @return the Base64-encoded string, as a <code>String</code> object
     */
    public static String encode(final Byte[] data) {
        final StringBuilder builder = new StringBuilder();
        final int dataRemainder = data.length % 3;

        int j = 0;
        int n = 0;
        for (; j < data.length; j += 3) {

            if (j < data.length - dataRemainder) {
                n = ((data[j] & 0xFF) << 16) + ((data[j + 1] & 0xFF) << 8) + (data[j + 2] & 0xFF);
            } else {
                if (dataRemainder == 1) {
                    n = (data[j] & 0xFF) << 16;
                } else if (dataRemainder == 2) {
                    n = ((data[j] & 0xFF) << 16) + ((data[j + 1] & 0xFF) << 8);
                }
            }

            // Left here for readability
            // byte char1 = (byte) ((n >>> 18) & 0x3F);
            // byte char2 = (byte) ((n >>> 12) & 0x3F);
            // byte char3 = (byte) ((n >>> 6) & 0x3F);
            // byte char4 = (byte) (n & 0x3F);
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 18) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 12) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) ((n >>> 6) & 0x3F)));
            builder.append(BASE_64_CHARS.charAt((byte) (n & 0x3F)));
        }

        final int bLength = builder.length();

        // append '=' to pad
        if (data.length % 3 == 1) {
            builder.replace(bLength - 2, bLength, "==");
        } else if (data.length % 3 == 2) {
            builder.replace(bLength - 1, bLength, "=");
        }

        return builder.toString();
    }

    /**
     * Determines whether the given string contains only Base64 characters.
     *
     * @param data
     *            the string, as a <code>String</code> object, to validate
     * @return <code>true</code> if <code>data</code> is a valid Base64 string, otherwise <code>false</code>
     */
    public static boolean validateIsBase64String(final String data) {
        if (data == null || data.length() % 4 != 0) {
            return false;
        }

        for (int m = 0; m < data.length(); m++) {
            final byte charByte = (byte) data.charAt(m);

            // pad char detected
            if (DECODE_64[charByte] == -2) {
                if (m < data.length() - 2) {
                    return false;
                } else if (m == data.length() - 2 && DECODE_64[(byte) data.charAt(m + 1)] != -2) {
                    return false;
                }
            }

            if (charByte < 0 || DECODE_64[charByte] == -1) {
                return false;
            }
        }

        return true;
    }

    /**
     * Private Default Ctor.
     */
    private Base64() {
        // No op
    }
}

